Marcus Mushroom is a member of the Mushroom Family. He only makes cameo appearances in "Larry-Boy and the Rumor Weed." He first appears sitting in the back of a car. He then appears going with the rest of his family to the library. Like his whole family, he believed the rumors about Alfred being a robot. They soon realized it wasn't true.
Marcus is a small gray mushroom. He has a small nose, mouth and eyes. His eyelids are colored gray, too. Marcus wears oval glasses and is about the same size as his brother, Angus.
- Himself in "Madame Blueberry"
- Himself in "Larry-Boy and the Rumor Weed" (cameo)